About half of American adults say they don't get enough sleep (only 30 percent report that they get, on average, at least six hours of sleep every day). Many of us rely on coffee or another source of caffeine to stay awake, and fewer of us take naps. And at least 45 percent of men polled believe that people can train themselves to need less sleep [source: Better Sleep Council, CDC].

Sorry guys, but we can't. Sleep isn't a waste of time, you won't sleep when you're dead and you can't train your body to function just fine on very little sleep. During combat, for instance, soldiers may need to remain awake for long periods of time, unable to get several hours at one time, perhaps needing to stay awake for 48 hours or longer. Research conducted by the Walter Reed Army Institute of Research found that despite all attempts, humans are unable to adapt to getting fewer hours of shut-eye than their body requires every day [source: Szivos]. Each of us has our own sleep requirement, and no matter how hard you try, your body isn't going to change its mind about that. You may stop noticing the effects of your sleep deprivation after a while, but less sleep is associated with heart disease and high blood pressure in addition to depression, diabetes, weight gain and even premature death.